1. Field of the Invention
The invention relates generally to medical devices and methods for their use. More particularly, the invention relates to systems and methods for ablating tissues or materials within the body.
2. Related Art
In the medical field, ablation is used as a therapy in the treatment of various diseases (e.g., skin spots, snoring, tumors, hemorrhage, arrhythmia, atherosclerosis) and has a number of modalities (e.g., DC, RF, microwave, laser, ultrasound, chemical, cryogenic, rotary blade).
An ablation can be performed to transect or otherwise alter the function of some tissue. For example, fatty deposits or plaque which present an obstruction in an artery can be removed using a laser to break up the obstruction, thereby restoring blood flow. In another example, cardiac muscle can be burned to create a lesion which obstructs the conduction of (aberrant) electrical signals within the heart (that is, the lesion interrupts abnormal electrical conduction in the heart, therefore cures abnormal heart rhythms.)
The treatment of cardiac arrhythmia is of particular interest, as it is debilitating or even deadly and is one of the most common disorders in clinical practice. In the United States, many patients die every year due to specific heart rhythm disorders that are caused by abnormal, rapid beats. For example, it is estimated that 3 million people in the United States have atrial fibrillation, one of the most common cause of stroke. Additionally, atrial fibrillation is also related to heart failure. A number of pharmacologic and surgical therapies are available to treat these disorders.
Percutaneous transluminal (catheter-based) ablation is a minimally invasive therapy and has been shown to be relatively safe and effective in treating selected heart rhythm disorders. In a typical cardiac ablation procedure, several catheters are advanced through the venous or arterial systems and positioned inside the heart. These are used to assess the etiology of the disease and then to treat it.
Various procedures are employed in catheter-based ablation therapy. Typically, a single percutaneous procedure to ablate cardiac tissue is iterative and makes use of multiple sheaths and catheters in multiple steps. First, catheters are maneuvered into various positions to denote the location and measure the timing of cardiac activation. This is followed by the placement of an ablation catheter in contact with the cardiac tissue at a location where electrical activity is to be disrupted. The ablation catheter is used to burn or freeze the engaged tissue, altering the tissue behavior. Additional measurements are then made to reassess the cardiac function. This process is performed iteratively, alternating measurement and ablation, until the cardiac activation and resulting heart rhythm are modified as desired.
Multiple factors affect the success of an ablation procedure. For example, because it is essential to have an accurate diagnosis of the type of arrhythmia and localization of the culprit(s) of the arrhythmia to achieve success in the ablation procedure, it is often necessary to place multiple electrode catheters in the heart. These catheters can interfere with one another as they are manipulated, and the use of multiple catheters can also increase the risks of clot formation and injury to the cardiac tissue.
Another factor is contact with the tissue to be ablated. Conventional devices such as those that use radio frequency energy, cryogenic material, and laser energy to ablate tissue are designed to ablate the target tissue when the catheter is in direct contact with the tissue. Tissue contact is critical, but various factors affect the contact and contact pressure between the tissue and ablation element, including the anatomy of the target and the adjacent structure, the design of the catheter itself, and the relationship between the catheter and the anatomy, to list only a few. Additionally, the presence of blood between the tissue and the ablation element severely decreases the efficacy of radio frequency, cryogenic, and laser ablation. The tissue characteristics can also affect the efficacy of the ablation energy. For instance, it is difficult for radio frequency and cryogenic materials to penetrate the superficial scar tissue and reach the deeper muscular tissue of interest.
Another factor affecting the success of an ablation procedure is the inability to reliably (re)position catheters. The positioning not only affects the ability to take consistent measurements with a recording electrode, but also affects the ability to reliably ablate the intended target tissue. For instance, mispositioning of the ablating element/electrode can result in failure to return to an ablation site to complete a burn (an ablation), or can result in gaps in a line of burns when creating a linear lesion. These factors can make it difficult to apply the therapy, render the therapy ineffective, or even enhance the disease (e.g., make the cardiac tissue proarrhythmic).
It would therefore be desirable to provide systems and methods for ablating tissue in the body which are less complicated and more reliable and effective than prior ablation systems and methods.